Liquid crystal display (LCD) screen and keypad brightness on a handheld electronic device may be adjusted for different operating environments in order to provide an optimal user experience. For example, in outdoor or sunlight conditions the LCD backlight must be very bright in order to be readable, and the keypad backlight should be off to conserver battery power. In normal indoor or office conditions, the LCD backlight should operate at medium brightness while the keypad backlight is usually turned off. In dim or dark conditions, the LCD backlight must be at low intensity so as to avoid eye strain and the keypad backlight must be on.
Ambient lighting conditions can change rapidly as the user moves between different working environments. For example, walking from indoors to outdoors may render the LCD screen immediately unreadable unless the LCD backlight brightness is increased. Conversely, when the user moves from a bright environment into a dimly lit room, the keypad may be unreadable unless the keypad backlight is turned on.
Prior art arrangements have been implemented in GPS displays and laptop computers for providing basic automatic screen and keypad backlighting adjustment. However, none of such prior art backlighting algorithms are known to address independent control of LCD and keypad backlighting adjustment as a user moves between different ambient lighting conditions. Moreover, none of the known prior art addresses the problem of providing rapid backlight adjustment in response to a user removing his or her handheld electronic device from a wearable holster accessory, or the problem of detecting ambient light when the light sensor and message notification indicator for the device share a common light pipe, such as described in co-pending U.S. patent application Ser. No. 11/187,867, filed Jul. 25, 2005, and entitled SHARED LIGHT PIPE FOR A MESSAGE INDICATOR AND LIGHT SENSOR.